The current development build (Adblock Plus 1.3.5b.2866) added support for Firefox Mobile 4.0 (many thanks to Fabrice Desré who did much of the work). Despite the significant architectural changes everything seems to work smoothly. As far as I know, there are only two issues:

Do-not-track support isn’t working. This isn’t going to change, with the current approach this feature would double the number of synchronous requests between content and chrome processes — not worth it.

We might be able to reduce the number of synchronous requests by using a cache, this should make things faster. To be done soon.

Other than that, the usual limitations apply — our user interface in Firefox Mobile is very limited, do not expect the same functionality as on the desktop. In particular, only one filter subscription at a time is supported.

Update: It only took five minutes after publishing this and I found one more issue: subscription selection page doesn’t come up on first install, you have to select a subscription in extension options manually. Update2: This will be fixed in the next development build (Adblock Plus 1.3.5b.2871).

Update3 (2011-03-18): Starting with Adblock Plus 1.3.5b.2886 all the issues on the first-run page should be fixed. The page layout is more what is expected for Firefox Mobile, the selection list can actually be used and confirming selection will only close the tab and not the entire browser.

Tried it with the nightly and build1 of the RC1 but the reporter doesn’t show up. :/

The description of the subscription window after restarting FF with ABP for the first time isn’t completely readable. The beginning is cut off. Tested with German locale.

Reply from Wladimir Palant:

I think the throttling rate for releases is around 1/10 – so you will need to submit 10 crash reports to get one processed :-(

The layout of the subscriptions page is incorrect, I know that. Fennec doesn’t like XUL in the browser at all. I asked Fabrice whether this can fixed somehow – we might simply have to live with it for now. In Adblock Plus 1.4 this page should be simplified once again, so it should work better then.

Reply from Wladimir Palant:

Never mind, I can see the “crash” – it’s actually the Fennec window being closed when only a tab should be closed, not an actual crash. I also made some progress on the layout of this dialog.

Wow, great job here. Ads are even more annoying on a smartphone than they are on a desktop computer.
Thanks for adding this support. Works great for me so far. (Didn’t test the first-run again, but those problems seem to solved as well.)
Thank you once again, Fabrice and Wladimir.